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ISSN 1480-4883© Her Majesty the Queen in Right of Canada, 2002

© Sa majesté la Reine, Chef du Canada, 2002

Research Document 2002/067 Document de recherche 2002/067

Not to be cited withoutpermission of the authors *

Ne pas citer sansautorisation des auteurs *

State of phytoplankton in the Estuaryand Gulf of St. Lawrence during 2001

État de phytoplancton dans l’estuaireet le golfe du Saint-Laurent en 2001

Michel Starr, Liliane St-Amand & Lyse Bérard-Therriault

Institut Maurice-LamontagneDirection des Sciences Océaniques

Ministère des Pêches et OcéansCP 1000, Mont-Joli, Québec, Canada G5H 3Z4

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Abstract

We review the information concerning the seasonal and interannual variations in the concentrationsof chlorophyll a, nitrates, and silicates as well as the abundance of the major species ofphytoplankton measured from three fixed stations and six sections crossing the Estuary and Gulf ofSt. Lawrence. We focus on the conditions prevailing in 2001 but compare those observations withprevious information from the period of 1992-2000.

In 2001, the initiation of the spring phytoplankton bloom at Station Rimouski in the Lower St.Lawrence Estuary occurred in early May, that is, 6-8 weeks earlier than usual. This continued atrend that began in 1998. This major shift in the timing of the phytoplankton cycle is believed to bedue to the below-normal spring freshwater runoff observed in the St. Lawrence basin since 1998.

For the second consecutive year, the average phytoplankton biomass at Station Rimouski duringspring-summer 2001 was much lower compared to the 1995-1999 period (except for 1998) butcomparable to the 1992-1994 period. In particular, the phytoplankton biomass in July 2001 wasmuch lower compared to our previous observations. This is believed to be due to a more intensemixing period in the Lower St. Lawrence Estuary in July 2001.

In the Anticosti Gyre and the Gaspé Current, the reduction of nutrients in the surface layer duringspring-summer-fall 2001 was much less pronounced compared to the 1996-1999 period (except for1998). In the Gaspé Current, near-surface chlorophyll levels were also generally lower in 2001compared to the previous two years. On the other hand, summertime chlorophyll levels in theAnticosti Gyre were higher in 2001 compared to those observed in 1997-2000.

Satellite observations of sea surface chlorophyll concentrations indicate that the 2001 spring bloomoccurred in late April for most areas of the Gulf of St. Lawrence. This contrasts with previousobservations showing a greater spatial variability in the timing of the bloom.

The analysis of community composition showed that the 2001 spring bloom over most of the Gulfwas principally dominated by the diatom Neodenticula seminae. This is the first occurrence of thisspecies in the Gulf of St. Lawrence; this species is usually found in North Pacific waters. Thisunusual event is consistent with recent observations indicating a greater influx of Pacific waters intothe Atlantic Ocean (via the Bering Strait) and with hydrographic evidence of a major intrusion ofLabrador Slope Water into the Gulf of St. Lawrence in 2001.

In late spring 2001, the chlorophyll levels were extremely low for most areas of the Gulf of St.Lawrence. The highest levels were observed in the nutrient-rich waters of the St. Lawrence Estuaryand Gaspé Current system. In the eastern and southern part of the Gulf, the chlorophyll and nitratelevels in the surface layer in late spring 2001 were not notably different than those observed in1999-2000.

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Résumé

Nous rapportons les variations saisonnières et interannuelles dans les concentrations de lachlorophylle a, les nitrates, et les silicates aussi bien qu’au niveau de la composition spécifique duphytoplancton dans l’estuaire et le golfe du Saint-Laurent. L’information présentée provient dedonnées mesurées à trois stations fixes et de six sections situées dans les diverses régions dugolfe et de l’estuaire du Saint-Laurent. Nous examinons plus particulièrement les conditionsprésentes en 2001 tout en les comparant aux observations pour la période de 1992-2000.

En 2001, l’initiation de la floraison printanière de phytoplancton à la station Rimouski dans l'estuairemaritime du Saint-Laurent s’est produite au début mai, soit 6-8 semaines plus tôt que la normale.Cette floraison printanière précoce poursuit la tendance initiée depuis 1998. Nous croyons que cechangement majeur dans le cycle du phytoplancton est dû aux débits d’eaux douces printaniersdans le Saint-Laurent qui ont été bien au-dessous de la normale depuis 1998.

Pour une deuxième année consécutive, la biomasse phytoplanctonique moyenne à la stationRimouski au cours du printemps et de l’été 2001 était beaucoup inférieure à celles observées aucours de la période 1995-1999 (excepté en 1998), mais néanmoins comparable à celles de lapériode 1992-1994. En particulier, la biomasse phytoplanctonique au mois de juillet 2001 étaitbeaucoup inférieure à celles précédemment observées. Nous croyons que ceci a été occasionnépar une période de mélange plus intense dans l'estuaire maritime du Saint-Laurent au cours dumois juillet 2001.

Dans la gyre d'Anticosti et le courant de Gaspé, la réduction des éléments nutritifs dans la couchede surface au cours de la période printemps-été-automne 2001 était beaucoup moins prononcéecomparée à la période 1996-1999 (excepté 1998). De plus dans le courant de Gaspé, les niveauxde chlorophylle en surface étaient généralement plus bas en 2001 comparés aux deux annéesprécédentes. D'autre part, les niveaux de chlorophylle estivale dans la gyre d'Anticosti étaient plusélevés en 2001 comparés à ceux observés en 1997-2000.

Les observations satellitaires en 2001 au niveau des concentrations en chlorophylle de surfaceindiquent que la floraison phytoplanctonique s'est produite à la fin d’avril pour la plupart des régionsdu golfe du Saint-Laurent. Ces observations diffèrent de celles acquises antérieurement quidémontrent une plus grande variabilité spatiale dans la période de la floraison phytoplanctonique.

L'analyse de la composition spécifique du phytoplancton a démontré que la floraisonphytoplanctonique de 2001 a été dominée par la diatomée Neodenticula seminae dans la plupartdes régions du Golfe. C'est la première occurrence de cette espèce dans le golfe du Saint-Laurent;cette espèce étant généralement retrouvée dans les eaux du Pacifique nord. Cet événement peucommun est consistant avec les observations récentes indiquant une plus grande intrusion deseaux du Pacifique nord dans l'océan Atlantique (par l'intermédiaire du détroit de Béring) et d'uneintrusion importante des eaux du Labrador dans le golfe du Saint-Laurent en 2001.

Au printemps 2001, les niveaux de chlorophylle étaient extrêmement bas pour la plupart dessecteurs du golfe du Saint-Laurent. Les niveaux les plus élevés ont été observés dans les eauxriches de l'estuaire du Saint-Laurent et du courant de Gaspé. Dans le nord-est et le sud du Golfe,les niveaux de chlorophylle et de nitrate dans la couche de surface n'étaient pas notammentdifférents au printemps 2001 que ceux observées au cours des deux dernières années.

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Introduction

This report presents the state of phytoplankton prevailing in the Estuary and Gulf of St. Lawrence in2001. Information is essentially derived from AZMP (Atlantic Zonal Monitoring Program) datacollected at a network of stations (fixed point stations and cross-shelf sections) sampled at afrequency of weekly to twice per year (Figure 1). Additional information from various researchprograms (SeaWIFS, cruises, Station Rimouski) are also used to complete this annual review.

Methods

Collections and standard measurements of nutrient and chlorophyll concentrations as well as thedetermination of phytoplankton composition are based on protocols outlined by the steeringcommittee of the Atlantic Zonal Monitoring Program (www.meds-sdmm.dfo-mpo.gc.ca).

Results and discussion

Lower St. Lawrence Estuary

The series of observations at Station Rimouski enable us to describe in more detail the inter-annualvariability in timing, duration, and magnitude of the spring phytoplankton bloom in the Lower St.Lawrence Estuary. This station has been visited on a weekly basis from May to September since1992 (Figure 2).

In 2001, the standing stock of phytoplankton at Station Rimouski, as reflected by the amount ofchlorophyll a (Figure 2), showed a major pulse in early May with integrated values in the upper 50m exceeding 200 mg of chlorophyll a / m2 (Figure 3). From late May to mid August, chlorophylllevels remained relatively low (<100 mg / m2) whereas a second major pulse was observed in lateAugust, with integrated values exceeding 300 mg of chlorophyll a per m2 (Figures 2 and 3).

Compared to our previous observations, the onset of the spring phytoplankton bloom at StationRimouski in 2001 occurred about the same time as in 1998 and 1999 (early May; Figures 2 and 4),but 6-8 weeks earlier compared to the 1992-1997 period (mid-June). A comparison of these resultswith historical data on the phytoplankton biomass in the lower St. Lawrence Estuary confirms thedevelopment of the primary bloom in early May as observed during the 1998-2001 period, isunusual for this region. Data near Station Rimouski for 1969-1971 (Steven 1974), 1974 (Sinclair1978), 1979-1980 (Levasseur et al. 1984), 1983-1984 (Starr et al. 1993), 1990 (Plourde and Runge1993), and 1991 (Runge and Joly; unpubl. data) showed the primary bloom starting between Juneand July.

Typically, the spring bloom in the lower St. Lawrence Estuary starts just after the spring-summerrunoff peak (e.g. Levasseur et al. 1984, Therriault and Levasseur 1985, Zakardjian et al. 2000).The below-normal spring freshwater runoff observed since 1998 in the St. Lawrence basin (notshown here) could thus be responsible for the recent shift seen in the timing of phytoplankton cycle.

Compared to our previous observations, the spring bloom duration at Station Rimouski was alsoshorter and less intense in 2001 compared to the 1995-1999 period (Figure 2). In contrast, thesecond phytoplankton bloom in late August was more intense in 2001 compared to our previousobservations. Nevertheless, for the entire sampling period, the average chlorophyll levels in theLower St. Lawrence Estuary during 2001 were, for the second consecutive year, much lowercompared to the 1995-1999 period but comparable to the 1992-1994 period (Figure 5). Inparticular, phytoplankton biomass in July 2001 was much lower compared to our previousobservations. This is believed to be due to a more intense mixing period in the Lower St. Lawrence

5

Estuary in July 2001, as indicated by CTD data and satellite images of temperature (not shownhere).

Northwestern Gulf of St. Lawrence

The northwestern Gulf of St. Lawrence is characterized by a quasi-permanent cyclonic gyre, theAnticosti Gyre. The Anticosti Gyre is separated from the Gaspé Current by a frontal system; theGaspé Current is a coastal jet resulting from the seaward advection of the low salinity waters fromthe St. Lawrence Estuary along the Gaspé Peninsula. These two systems represent two identifiablepelagic ecosystems. The biological and chemical properties of the Gaspé Current reflect theconditions developing in the Lower Estuary whereas those found in the Anticosti Gyre are moretypical of the conditions prevailing over the Gulf of St. Lawrence proper (Levasseur et al. 1992).Within the AZMP, these two systems are monitored at a frequency of 9 to 19 times per year.

In 2001, nutrient concentrations in the surface layer (top 50 m) followed a similar seasonal patternat both stations in the northwestern Gulf of St. Lawrence: nitrate and silicate concentrations werehigh in late fall-winter and low in spring-summer due to biological consumption by phytoplankton(Figure 6). Typically, nutrient concentrations were somewhat higher in the Gaspé Current than inthe Anticosti Gyre and more variable due to the dynamics of this coastal jet. The spring decrease inthe surface nutrients occurred approximately 2-3 weeks earlier in the Anticosti Gyre than in theGaspé Current (Figure 6), suggesting that phytoplankton growth may have been initiated somewhatearlier in the Gyre.

In the Gaspé Current, the spring decrease of nitrate and silicate coincided with the first pulse ofphytoplankton at Station Rimouski (early May) and also with the small increase in the chlorophyllconcentration in the Current’s low salinity surface waters (Figures 2 and 6). From early June to lateJuly, chlorophyll levels remained relatively low (<70 mg / m2) whereas a second major pulse wasobserved in August (i.e. about same time as the one observed at Station Rimouski), with integratedvalues exceeding 200 mg of chlorophyll a / m2 (Figures 6 and 7). Finally, a third smallerphytoplankton peak was observed during fall 2001 (mid October), which is typical.

In the Anticosti Gyre, near-surface chlorophyll concentrations remained low throughout thesampling period except in late April, when a small spring bloom of short duration was observed(Figure 6). A deep chlorophyll maximum layer was nevertheless observed at 35 m from late June tolate August at the base of the nutricline (Figure 6). The activity of the phytoplankton assemblage inthe deep chlorophyll maximum layer at this time would be limited due to irradiance levelsapproaching the 1% light level.

Overall, the chlorophyll a levels in the Gaspé Current were lower in 2001 than in 1999 and 2000 butcomparable to 1996 and 1997 (Figure 7). In contrast, the subsurface chlorophyll levels duringsummer 2001 in the Anticosti Gyre were much higher compared to our previous observations(Figure 8). On the other hand, the nitrate concentrations in the near-surface waters in late winter2001 at both stations were comparable to those observed in 2000 but lower than those in 1996-1999 (except for 1998) while the summer concentrations were comparable (Figures 7 and 8).Moreover, the reduction of nutrients during fall 2001 in the Anticosti Gyre was much lesspronounced compared to 1999 and 2000 (Figure 8). Based on the seasonal reduction of nutrients,phytoplankton production in the northwestern part of the Gulf of St. Lawrence would probably havebeen lower in 2001 compared to the previous two years.

6

Other regions of the Gulf

Sections. Chlorophyll and nutrient data were collected at 41 stations along six sections crossingthe Estuary and the Gulf of St. Lawrence (Figure 9) to obtain quasi-synoptic information on abroader spatial coverage. Sections were occupied during late spring (June) and late fall(December) 2001 (Figure 1). This sampling program has been in place since 1999. Analysis of the2001 fall samples is not yet completed.

Nitrate concentrations in the late spring 2001 increased with depth for the most areas of the Gulf ofSt. Lawrence (Figure 9). The concentrations at depth (> 200 m) increased from Cabot Strait towardthe head of the Laurentian Channel in the Lower St. Lawrence Estuary, a gradient that probablyresults from the circulation and mineralization of organic matter that sinks into the deep layer(Coote & Yeats 1979, Savenkoff et al. 2001). Compared to previous years, nitrate concentrations inthe deep layer in 2001 were comparable to those in 2000, but higher than in 1999 (not shownhere).

Silicate concentrations also increased with depth but to a greater degree than did nitrate (Figure10), which is typical for the Gulf of St. Lawrence (Steven 1974, Savenkoff et al. 2001). The averagesilicate concentration in the deep water of Cabot Strait and the eastern part of the Gulf was 20mmol / m3 while values exceeding 45 mmol / m3 occurred near the bottom in the Estuary. Theseunusually high values compared to adjacent waters are thought to be due to precipitationprocesses and sedimentation of silica from the river water. Compared to previous years, silicateconcentrations in the deep layer in the late spring 2001 were comparable to 2000 but lower than in1999 (not shown here).

In the surface layer, spring nitrate and silicate concentrations were uniformly low in 2001 for mostregions of the Gulf of St. Lawrence (Figures 9 and 10). Nevertheless, there was a gradual decreasein the depth over which nutrient depletion occurred from Cabot Strait to the Estuary along theLaurentian Channel, indicating that nutrients moving from the Estuary toward Cabot Strait weregradually incorporated into plankton. The depletion of nutrients in the surface layers was also morepronounced in the eastern and southern part of the Gulf of St. Lawrence compared to the Estuaryand northwestern part of the Gulf, which is typical (e.g. Steven 1974).

Compared to our previous observations, the amounts of nitrate in the top 50 m in the southern andeastern Gulf were not markedly different during the spring 2001 than in 1999-2000 (Figure 11). Incontrast, the nitrate depletion in the surface layers was generally less pronounced in thenorthwestern Gulf during late spring 2001 than in 1999 and 2000.

Chlorophyll levels during the spring of 2001 were low except for the estuarine portion of Gulfincluding the St. Lawrence Estuary and Gaspé Current system (Figure 12), which is typical (e.g.Steven 1974). In 2001, the chlorophyll levels in the eastern and southern part of the Gulf were notmarkedly different from those in 1999-2000 (Figure 13).

Satellite observations. Phytoplankton biomass was also assessed from ocean color datacollected by the Sea-viewing Wide Field-of-View (SeaWiFS) satellite sensor launched by NASA inlate summer 1997. Satellite data do not give information for the water column but provide high-resolution (1.5 km) data on the geographical distribution of phytoplankton in surface waters over alarge scale. Composite images over two-week intervals for the Gulf of St. Lawrence can be foundat the Bedford Institute of Oceanography Ocean Sciences Division website (http//www.mar.dfo-mpo.gc.ca/science/ocean/ias/seawifs_1.html). Note that data for the estuarine portion of the Gulfare uncertain (due to humic substances) and must be used with caution.

Satellite data revealed that the 2001 spring bloom occurred in late April for most areas of the Gulfof St. Lawrence (not shown here). This contrasts with our previous observations, which showed a

7

greater spatial variability in the timing of the spring bloom. During late spring-summer, chlorophylllevels remained low for most areas of the Gulf (except for the estuarine portion), which is consistentwith observations from the fixed stations and sections crossing the Gulf. Another smallerphytoplankton peak was observed in the fall for the most areas of the Gulf (October), which isusual.

Research cruise. During a research cruise in late April, phytoplankton samples were collectedat 16 stations covering the Estuary and Gulf of St. Lawrence. The analysis of these samplesrevealed that the 2001 spring bloom in the Gulf of St. Lawrence was essentially dominated by thediatom Neodenticula seminae (Figure 14). This is the first occurrence of this species in the Gulf ofSt. Lawrence; this species is usually found in North Pacific waters (Yanagisawa and Akiba 1990).In the Atlantic Ocean, this species has only been recorded in high-latitude Quaternary sedimentsbetween 0.84 and 1.26 Ma (Baldauf 1986). Because this unusual spring bloom coincided with amassive intrusion of Labrador Slope Waters into the Gulf of St. Lawrence (Gilbert 2002, Harvey etal. 2002), we suppose that this Pacific species was introduced naturally into the Gulf (across theArctic and down the Labrador current), rather than via ballast waters. This is consistent with recentobservations indicating a greater influx of Pacific waters into the North Atlantic and changes in thecirculation and oceanographic conditions in the Arctic Ocean (Dickson 1999).

Conclusions

Seasonal patterns and regional differences were observed in the concentrations of chlorophyll,nitrates and silicates as well as the phytoplankton composition in the Estuary and Gulf of St.Lawrence in 2001. Prominent events in 2001 included: 1) the initiation of the spring phytoplanktonbloom in the Lower St. Lawrence Estuary occurred, for a fourth consecutive year, 6-8 weeks earlierthan usual; 2) the phytoplankton biomass during spring-summer 2001 in the Lower St. LawrenceEstuary was, for a second consecutive year, much lower compared to the 1995-1999 period; 3) thesatellite data revealed for the first time, little differences in the timing of the 2001 spring bloom inthe Gulf of St. Lawrence and 4) the first occurrence of the diatom Neodenticula seminae in theregion; this species is usually observed in North Pacific waters.

Acknowledgements

We thank Laure Devine, Marie-Lyne Dubé, Alain Gagné, Yves Gagnon, and Pierre Joly for theirsteadfast work on this project. The taxonomic expertise of the Dr. Michel Poulin was crucial for thecompletion of this work.

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References

Baldauf J.G. (1986). Diatom biostratigraphic and paleoceanographic interpretations for the middleto high latitude North Atlantic Ocean. In: Summerhayes C.P. and N.J. Shackleton (eds) NorthAtlantic Paleoceanography, Geological Society Special Publication No. 21, pp. 243-252.

Coote A.R. and P.A. Yeats (1979). Distribution of nutrients in the Gulf of St. Lawrence. Journal ofthe Fisheries Research Board of Canada 36: 122-131.

Dickson B. (1999). Oceanography: All change in the Arctic. Nature 397: 389-391.

Gilbert D. (2002). Oceanographic conditions in the Gulf of St. Lawrence in 2001. DFO ScienceStock Status Report (in prep.)

Harvey M., St-Pierre J.F., Joly P. & G. Morrier (2002). Oceanographic conditions in the Estuary andthe Gulf of St. Lawrence during 2001: zooplankton. DFO RES DOC 2002/046, 29 p.

Levasseur M., Fortier L., Therriault J.-C. and P. Harrison (1992). Phytoplankton dynamics in acoastal jet frontal region. Marine Ecology Progress Series 86: 283-295.

Levasseur M., Therriault J.-C. and L. Legendre (1984). Hierarchical control of phytoplanktonsuccession by physical factors. Marine Ecology Progress series 19: 211-222.

Plourde S. and J. A. Runge (1993). Reproduction of the planktonic copepod Calanus finmarchicusin the Lower St. Lawrence Estuary: relation to the cycle of phytoplankton production and evidencefor a Calanus pump. Marine Ecology Progress Series 102: 217-227.

Savenkoff C., Vézina A.F., Smith P.C. and G. Han (2001). Summer transports of nutrients in theGulf of St. Lawrence estimated by inverse modelling. Estuarine, Coastal and Shelf Science 52:565-587.

Sinclair M. (1978). Summer phytoplankton variability in the lower St. Lawrence Estuary. Journal ofthe Fisheries Research Board of Canada 35: 1171-1185.

Starr M., Himmelman J.H. and J.-C. Therriault (1993). Environmental control of green sea urchin,Strongylocentrotus droebachiensis, spawning in the St. Lawrence Estuary. Canadian Journal ofFisheries and Aquatic Sciences 50: 894-901.

Steven D. M. (1974). Primary and secondary production in the Gulf of St. Lawrence. McGillUniversity Marine Science Center MS Report. 26:116 p.

Therriault J.-C. and M. Levasseur (1985). Control of phytoplankton production in the Lower St.Lawrence Estuary: light and freshwater runoff. Naturaliste canadien 112: 77-96.

Yanagisawa Y. and F. Akiba (1990). Taxonomy and phylogeny of three marine diatom genera,Crucidenticula, Denticulopsis and Neodenticula. Bulletin of the Geological Survey of Japan 41: 197-301.

Zakardjian A.B., Gratton Y. and A. F. Vezina (2000). Late spring phytoplankton bloom in the LowerSt. Lawrence Estuary: the flushing hypothesis revisited. Marine Ecology Progress Series 192: 31-48.

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Figure 1. Dates of 2001 sampling at the Atlantic Zonal Monitoring Program (AZMP) sections(lines) and fixed stations (dots).

0 30 60 90 120 150 180 210 240 270 300 330 360

Ja n Fe b M ar Apr May J un J ul Aug Sep Oc t Nov Dec

Day of the year

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Figure 2. Chlorophyll a concentration (mg / m2) at the Rimouski station during the period MaySeptember between 1992 and 2001. The black dots over each graph indicate theprecise date of sampling.

120 140 160 180 200 220 240 260 280 Day of the year

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Figure 3. Chlorophyll a concentrations (mg / m2) integrated over the upper 50 m at StationRimouski during spring-summer 1992-2001.

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Figure 4. Date of onset of the primary bloom defined by the first incidence of chlorophyllconcentrations greater than 100 mg of chlorophyll a per m2 at Station Rimouski, 1992-2001.

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Figure 5. Mean integrated (surface to 50m depth) chlorophyll a levels at Station Rimouski fromMay to August, 1992-2001.

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Figure 6. Vertical profiles of chlorophyll a (mg/m3), nitrate (µM) and silicate (µM) concentrationsin the Gaspé Current and Anticosti Gyre during 2001. The black dots over each graphindicate the precise data of sampling.

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Figure 7. Nitrate (mmol / m2) and chlorophyll a (mg / m2) concentrations in the Gaspé Current,1996-2001. Values are integrated over the upper 50 m of the water column.

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Figure 8. Nitrate (mmol / m2) and chlorophyll a (mg / m2) concentrations in the Anticosti Gyre,1996-2001. Values are integrated over the upper 50 m of the water column.

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Figure 9. Concentrations of nitrate (mmol / m3) versus depth along the six sections sampled inJune 2001 in the Estuary and Gulf of St. Lawrence. The numbers over each graphindicate the location of sampling stations. Red circle : starting point.

70° 68° 66° 64° 62° 60° 58° 56°

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Magdalen Island

-70

-60

-50

-40

-30

-20

-10

0

Dep

th (m

)

Nitrate levels (June 2001)

mmol / m3

1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 1 2 3 4 5 6 7

1 2 3 4 521 3 4 5 6 7 1 2 3 4 5 6

O

O

O

O

O

O

18

Figure 10. Concentrations of silicate (mmol / m3) versus depth along the six sections sampled inJune 2001 in the Estuary and Gulf of St. Lawrence. The numbers over each graphindicate the location of sampling stations. Red circle : starting point.

70° 68° 66° 64° 62° 60° 58° 56°

46°

48°

50°

52°

NEWFOUNDLAND

NEW BRUNSWICK

ANTICOSTI

QUEBEC

0 10 20 30 40 50Distance (Km)

St. Lawrence Estuary

-300

-250

-200

-150

-100

-50

0

Dep

th (m

)

024681015202530354045

0 20 40 60 80 100Distance (Km)

Sept-Îles

-300

-250

-200

-150

-100

-50

0

0 20 40 60 80Distance (Km)

Anticosti

-300

-250

-200

-150

-100

-50

0

0 50 100 150Distance (Km)

Bonne Bay

-300

-250

-200

-150

-100

-50

0

0 50 100Distance (km)

Cabot Strait

-300

-250

-200

-150

-100

-50

0

0 100 200 300Distance (km)

Magdalen Island

-70

-60

-50

-40

-30

-20

-10

0

Dep

th (m

)

mmol / m3

Silicate levels (June 2001)

21 3 4 5 6 7 1 2 3 4 5 6 1 2 3 4 5

1 2 3 4 5 6 71 2 3 4 5 61 2 3 4 5 6 7 8 9 10

O

O O

O

OO

19

Figure 11. Nitrate concentrations (mmol / m2) along the six sections sampled in June in theEstuary and Gulf of St. Lawrence, 1999-2001. Values are integrated over the upper 50m of the water column.

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St. Lawrence Estuary

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7

Nitr

ate

(mm

ol /

m2 )

Mean ± std2001: 437.8 ± 76.4

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Sept-Îles

0

100

200

300

400

500

600

700

1 2 3 4 5 6

Mean ± std1999: 147.3 ± 89.52000: 200.3 ± 46.5 2001: 247.9 ± 106.0

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Anticosti

0

100

200

300

400

500

600

700

1 2 3 4 5

Nitr

ate

(mm

ol /

m2 )

Mean ± std1999: 94.1 ± 35.02000: 149.1 ± 58.42001: 174.2 ± 54.4

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Bonne Bay

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7

Mean ± std1999: 54.9 ± 37.92000: 71.0 ± 28.2 2001: 54.9 ± 32.1

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Cabot Strait

0

100

200

300

400

500

600

700

1 2 3 4 5 6Station

Nitr

ate

(mm

ol /

m2 )

Mean ± std1999: 45.0 ± 17.72000: 90.8 ± 62.12001: 65.7 ± 31.9

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Magdalen Island

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10Station

Mean ± std1999: 77.1 ± 42.5 2000: 148.9 ± 103.5 2001: 77.4 ± 61.2

20

Figure 12. Concentrations of chlorophyll a (mg / m3) versus depth along the six sections sampledin June 2001 in the Estuary and Gulf of St. Lawrence. The numbers over each graphindicate the location of sampling stations. Red circle : starting point.

0 10 20 30 40 50Distance (Km)

St. Lawrence Estuary

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Dep

th (m

)

0123456789101112

0 20 40 60 80Distance (Km)

Anticosti

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 20 40 60 80 100Distance (km)

Cabot Strait

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 20 40 60 80 100Distance (Km)

Sept-Îles

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 50 100 150Distance (Km)

Bonne Bay

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 100 200 300Distance (km)

Magdalen Island

-70

-60

-50

-40

-30

-20

-10

0

Dep

th (m

)

70° 68° 66° 64° 62° 60° 58° 56°

46°

48°

50°

52°

NEWFOUNDLAND

NEW BRUNSWICK

ANTICOSTI

QUEBEC

Chl levels (June 2001)

mg/m3

21 3 4 5 6 7

1 2 3 4 5 6 71 2 3 4 5 61 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 1 2 3 4 5

O

O

O

OO

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21

Figure 13. Chlorophyll a concentrations (mg / m2) along the six sections sampled in June in theEstuary and Gulf of St. Lawrence, 1999-2001. Values are integrated over the upper 50m of the water column.

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St. Lawrence Estuary

0

50

100

150

200

250

300

350

1 2 3 4 5 6 7

Chl

(mg

/ m2 )

Mean ± std 2001: 174.3 ± 98.8

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0

50

100

150

200

250

300

350

1 2 3 4 5 6

Mean ± std1999: 48.3 ± 28.32000: 14.5 ± 7.92001: 48.3 ± 19.8

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0

50

100

150

200

250

300

350

1 2 3 4 5

Chl

(mg

/ m2 )

Mean ± std1999: 48.7 ± 20.92000: 42.2 ± 44.5 2001: 33.2 ± 12.8

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0

50

100

150

200

250

300

350

1 2 3 4 5 6 7

Mean ± std1999: 29.2 ± 11.32000: 23.0 ± 23.8 2001: 12.2 ± 3.4

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0

50

100

150

200

250

300

350

1 2 3 4 5 6 7 8 9 10Station

Mean ± std1999: 32.1 ± 18.02000: 13.4 ± 1.52001: 27.8 ± 7.1

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Cabot Strait

0

50

100

150

200

250

300

350

1 2 3 4 5 6Station

Chl

(mg

/ m2 )

Mean ± std1999: 68.2 ± 41.72000: 15.2 ± 4.72001: 23.4 ± 8.3

22

Figure 14. Abundances (cells/L) of the diatom Neodenticula seminae in late April 2001 in theEstuary and Gulf of St. Lawrence.

70° 68° 66° 64° 62° 60° 58° 56°

46°

48°

50°

52°

Neodenticula sp.

0 to 1000

1000 to 10000

10000 to 100000

100000 to 1000000

1000000 to 10000000

NEWFOUNDLAND

NEW BRUNSWICK

ANTICOSTI

QUEBEC

< 1,0001,000 - 10,00010,000 - 100,000

100,000 - 1,000,000>1,000,000

Neodenticula seminaecells/L